Glide path indicators (GPIs), which are also known as glide path indicators, visual glide slope indicators (VGSIs), and visual glideslope indicators, are devices that use one or more lights or light emitters to assist a pilot in landing an airplane, for example, at an airport, ship flight deck, oil and gas platform flight deck or on an aircraft carrier.
The lights of a glide path indicator provide visual descent guidance to a pilot of an aircraft during landing of that aircraft on a runway by defining a vertical glide path, or approach path. The glide path indicator may indicate to the pilot whether that aircraft is too high, too low, or established on the proper descent profile for an optimum landing.
It is known to stabilise glide path indicators used onboard ships (e.g. aircraft carriers) to account for motion of the ship such that a constant (i.e. unchanging) glide path is indicated to the pilot of an approaching aircraft.